The repair of gas mains can present substantial hazards to workmen and others in the vicinity who are exposed to large volumes of gas if the main is not effectively sealed off against leakage. Various types of inflationary bags have been devised to stop-off cast iron and large diameter steel pipe and, while these have been designed to discourage any tendency to be blown downstream due to slippage or leakage, have not been completely failsafe in use. Moreover, a serious problem in connection with the installation of inflationary bags is the loss of gas through the sidewall of the pipeline when the bag or other restraining device is being installed. For example, ALH Systems, Inc. of Wiltshire, England manufactures and sells stop-off equipment including Gas Bags in which the bag is assembled around a flexible central inflation rod to discourage the bag from slipping along the interior of the pipeline under gas pressure once the bag has been inflated into the desired position. Such bags are satisfactory from the standpoint of sealing off the interior of the pipeline but do not avoid the risk of slipping or being blown downstream through the pipeline under gas pressure and thus not effectively seal the interior of the line.
U.S. Pat. No. 4,627,470 to Carruthers is directed more to the use of primary and secondary bags which are independently inserted into a pipeline to be repaired with the primary bag being inserted into position against a support disk and the secondary bag mounted directly against a column which is inserted through a hole in the pipe but does not address the problem of sealing off the wall of the pipe during the insertion of the bags, support disks and column and to adequately cap off the insertion holes once the job is completed. U.S. Pat. No. 4,428,204 to Brister discloses the use of a bag which is inserted through an insertion apparatus, and the bag is filled with water and frozen in place. U.S. Pat. No. 4,827,984 to Young et al utilizes an inflatable plug inserted into a pipeline but which is primarily designed for use in oil platform applications. U.S. Pat. No. 4,458,721 to Yie et al discloses an inflatable sleeve for restricting fluid flow in a pipeline using different forms of cartridges.
Notwithstanding the various approaches that have been taken in the past, there is a continuing need and demand for a novel and effective method and means for sealing off sections of a gas main and in which the gas main is sealed off from leakage or escape of gas throughout the entire operation beginning with the insertion of sealing devices into the line and concluding with removal of the sealing devices and particularly the inflation bags once the job is completed.